AMR-type integrated magnetoresistive sensor for detecting magnetic fields perpendicular to the chip

ABSTRACT

An AMR-type integrated magnetoresistive sensor sensitive to perpendicular magnetic fields is formed on a body of semiconductor material covered by an insulating region. The insulating region houses a set/reset coil and a magnetoresistor arranged on the set/reset coil. The magnetoresistor is formed by a magnetoresistive strip of an elongated shape parallel to the preferential magnetization direction. A concentrator of ferromagnetic material is arranged on top of the insulating region as the last element of the sensor and is formed by a plurality of distinct ferromagnetic regions aligned parallel to the preferential magnetization direction.

BACKGROUND

Technical Field

The present disclosure relates to an integrated magnetoresistive sensorof an AMR (anisotropic magnetoresistance) type for detecting magneticfields perpendicular to the chip integrating the magnetoresistivesensor. In particular, the magnetoresistive sensor may be integratedwith other magnetoresistors sensitive to magnetic fields parallel to thechip for forming a triaxial magnetometer integrated in a single chip.

Description of the Related Art

AMR-type magnetic-field sensors are used in a plurality of applicationsand systems, for example in compasses, in ferromagnetic characteristicsdetecting systems, in detection of currents, and in a wide range ofother applications, by virtue of their capacity of detecting naturalmagnetic fields (for example, the Earth's magnetic field) and magneticfields generated by electrical components (such as electrical orelectronic devices and lines passed by electric currents).

As known, magnetoresistive sensors exploit the capacity of appropriateferromagnetic materials (referred to as “magnetoresistive materials”,for example, the material known by the term “permalloy” formed by a FeNialloy) of modifying their own resistance in presence of an externalmagnetic field.

Integrated magnetoresistive sensors are known having the form of stripsof magnetoresistive material arranged on a substrate of semiconductormaterial, for example silicon. During manufacture, the magnetoresistivematerial strip is magnetized so as to have a preferential magnetizationin a preset direction, referred to as “easy axis” since it is thedirection of easier magnetization of the strip, typically thelongitudinal direction of the strip.

In the absence of external magnetic fields, the magnetization maintainsthe set direction, and the strip has a maximum resistance. In presenceof external magnetic fields that have a direction different from thepreferential magnetization direction, the strip magnetization changes,as well as its resistance, which decreases, as shown in FIGS. 1A and 1B.

In FIG. 1A, a magnetoresistor 1 is formed by a magnetoresistive strip 2having a longitudinal direction parallel to axis X and forming the easyaxis. The magnetoresistor 1 is supplied with a current I flowing in thelongitudinal direction of the strip. In the shown condition, in theabsence of external magnetic fields, the magnetization M is directedparallel to the easy axis EA.

In FIG. 1B, the magnetoresistor 1 is immersed in an external magneticfield Hy directed parallel to axis Y (referred to as also “hard axis”,i.e., the axis of more difficult magnetization of the magnetoresistivestrip 2). In this condition, the external magnetic field Hy causes arotation of the magnetization M through an angle α with respect to thecurrent I, causing a reduction of the resistance of the magnetoresistivestrip 2 according to a law correlated to cos² α.

In order to linearize the plot of the resistance R at least in anoperating portion of the curve, it is further known to form, on themagnetoresistive strip 2, transverse strips 3 (referred to as “barberpoles”), of conductive material (for example, aluminum), which arearranged with an inclination of 45° with respect to the direction ofeasy axis EA, as shown in FIG. 2.

In this situation, the direction of the current I changes, but not themagnetization M (the direction whereof still depends upon the externalmagnetic field), and the resistance has a linear characteristic aroundthe zero point of the external magnetic field. In this way, possiblemagnetic fields directed along or having a component parallel to axis Ymay be detected easily.

FIG. 3 shows a magnetoresistive sensor including four magnetoresistors 1of the type illustrated in FIG. 2, connected to form a Wheatstone bridge4. In the illustrated example, the Wheatstone bridge 4 comprises twomagnetoresistors 1 a having transverse strips 3 directed at +45° and twomagnetoresistors 1 b having transverse strips 3 directed at −45°. Themagnetoresistors 1 a, 1 b are arranged in an alternating way in eachbranch 4 a and 4 b of the bridge. The two branches 4 a, 4 b areconnected at two input nodes 5, 6 and a biasing voltage Vb is appliedacross them.

In this way, in the absence of external magnetic field componentsparallel to the sensing direction (here the field Hx), the outputvoltage Vo across the output terminals 7, 8 is, to a firstapproximation, zero. Instead, an external magnetic field Hx causes anincrease of the resistivity of two magnetoresistors, for example themagnetoresistors 1 a, and a corresponding reduction of the resistivityof the other magnetoresistors, for example the magnetoresistors 1 b,causing an unbalancing of the Wheatstone bridge 4 and a non-zero outputvoltage Vo. Consequently, each variation of resistance due to anexternal field Hx parallel to the plane of the magnetoresistors 1 a, 1 band perpendicular to their extension direction causes a correspondinglinear variation of the output voltage Vo.

When it is desired to detect magnetic fields that have componentsdirected along any direction parallel to the main faces of the chipintegrating the magnetoresistor (plane XY), it is possible to arrangethe magnetoresistors 1 perpendicular to each other, as shown in thesensor 10 of FIG. 4 where, for simplicity, a magnetoresistor 1 x, fordetecting the component X, and a magnetoresistor 1 y, for detecting thecomponent Y, are shown. Obviously, each magnetoresistor 1 x, 1 y of FIG.4 may be replaced by a respective Wheatstone bridge similar to that ofFIG. 3, wherein the four magnetoresistors 1 x are directed perpendicularto the four magnetoresistors 1 y.

By virtue of the high sensitivity of the magnetoresistive sensors of thetype referred to above, they have been proposed for use as electroniccompasses in navigation systems. In this case, the external field to bedetected is represented by the Earth's magnetic field. To a firstapproximation, the Earth's magnetic field may be considered parallel tothe Earth's surface, and reading of the compass may be made using thesensor 10, where X and Y represent the two directions of the planelocally tangential to the Earth's surface. However, since theinclination of the compass with respect to the tangential plane causesreading errors, in order to correct it, it is practical to have threesensors, each sensitive to a respective axis X, Y, Z.

To this end, some compasses integrate the X and Y sensors in a singlechip, and the latter is fixed parallel to a base or frame, and the Zsensor, manufactured in a planar way, like the X and Y sensors, in asuitable chip, is fixed to the frame rotated through 90°, in a verticalposition. However, in this case, the assembly is complex, and the enddevice is costly. Further, the packaged device has an excessive volume(in particular an excessive height), which does not enable use thereofin small apparatus.

In order to solve the above problem, a ferromagnetic concentrator hasbeen proposed, arranged alongside a planar magnetoresistor and directedtransversely to the sensitivity plane of the magnetoresistor (see, forexample, U.S. Patent Publication No. 2013/0299930 and U.S. PatentPublication No. 2014/0159717). For a better understanding, reference maybe made to FIG. 5, showing a magnetoresistive sensor 15 formed accordingto the teachings of above patent application TO2012A001067 in a chiphaving a substrate 16 of conductive material, for example silicon, andan insulating layer 17. The substrate 16 has a main face 20, which isplanar, and the insulating layer 17 houses a magnetoresistor 18, whichextends parallel to the main face 20. The magnetoresistor 15 is formedas shown in FIG. 2 and thus comprises a magnetoresistive strip 2 andtransverse strips 3 (only one whereof is visible).

A concentrator 21 of soft ferromagnetic material (i.e., one that may beeasily magnetized and does not maintain the magnetization after removalof the external magnetic field) extends in a trench 22 in the substrate17. The concentrator 21 here has a U shape, the arms whereof extendparallel to axis Z and have a length much greater than its thickness.One of the arms of the concentrator 21 extends also in the insulatinglayer 17, as far as in the proximity or even in contact with themagnetoresistor 15. In an embodiment where the concentrator is in directelectrical contact with the magnetoresistor, to prevent the currentflowing in the magnetoresistor from getting lost in the concentrator,the latter is discontinuous.

Consequently, when the magnetoresistive sensor 15 is subject to anexternal magnetic field Hz directed along axis Z, the arm of theconcentrator 21 in contact with the magnetoresistor 18 causes aconcentration and deflection of the field lines in horizontal direction(in plane XY) and generation of a horizontal field component Hy directedin the sensing direction. A reading circuit may then detect resistancevariations of the magnetoresistor 15 in a known way.

This solution, although enabling detection of magnetic fieldsperpendicular to the chip with an arrangement of the magnetoresistorparallel to the fixing frame, may undergo improvement.

In fact, to form the concentrator 21 in the substrate 16, it ismanufactured prior to forming the magnetoresistor 18 by forming thetrench 22 and coating the walls thereof with a thin layer offerromagnetic material. The step of depositing the ferromagnetic layeris not, however, simple because of the high aspect ratios. Further, inorder to form the further structures of the device, the trench is filledwith oxide. However, in some cases, the filling operations may entaillimitations in treatment temperatures when forming structures after theconcentrator, so as to prevent a reduction of the magnetic properties ofthe concentrator 21.

BRIEF SUMMARY

According to one embodiment of the present disclosure, an AMR-typeintegrated magnetoresistive sensor sensitive to perpendicular magneticfields includes a semiconductor body, an insulating region, a set/resetcoil, a first magnetoresistor, and a concentrator. The semiconductorbody has a face extending in a plane, the insulating region is on theface of the body, and the set/reset coil is arranged within theinsulating region. The first magnetoresistor is arranged within theinsulating region and on the set/reset coil and includes an elongatedfirst magnetoresistive strip extending longitudinally in a firstdirection. The concentrator is of ferromagnetic material, is arranged onthe insulating region, and is formed by a plurality of distinctferromagnetic regions aligned with each other parallel to the firstdirection.

In one embodiment, the concentrator is formed as the last element of thechip or die, immediately prior to passivation. Further, the set/resetcoil, intended for “refresh” operations to maintain the magnetizationset on the magnetoresistor in absence of external fields, is formed asthe first element, underneath the magnetoresistor, by reversing thestack in the magnetoresistors, which normally envisage forming theset/reset coil as last element. Consequently, a planarized oxide layeris formed on the turns of metal material defining the set/reset coil,the magnetoresistor with its magnetic strips is formed over the oxidelayer, and the concentrator is formed on top of the magnetoresistor.With this arrangement, the concentrator is closer to the sensitiveregions but the flux lines generated by the set/reset coil during therefresh step could be deviated by the concentrator in a not usefuldirection, thus reducing the efficiency of the set/reset operation. Toprevent this, the concentrator is formed in a discontinuous or discreteway, via a plurality of “bars” or parallelepipedal regions alignedparallel to extension axis of the magnetoresistor. In this way, themagnetoresistor and the concentrator are very close to each other, ahigh concentration effect and a high sensitivity to magnetic fields indirection Z are obtained, and the set and reset procedures are notsignificantly affected.

According to another aspect of the disclosure, each magnetoresistorcomprises two magnetoresistive strips parallel to each other, and theconcentrator extends in a midplane therebetween.

According to yet another aspect of the disclosure, the twomagnetoresistive strips are the same to each other, having the samedimensions (width, length, and thickness) and being of the samematerial, so that the midplane also forms a symmetry plane for the twomagnetoresistive strips that enables rejection of field componentsperpendicular to the sensing direction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure preferredembodiments thereof are now described, purely by way of non-limitingexample, with reference to the attached drawings, wherein:

FIGS. 1A and 1B show schematically a known AMR-type magnetoresistor inabsence and, respectively, presence of an external magnetic field;

FIG. 2 shows schematically an embodiment of a known AMR magnetoresistorhaving barber poles;

FIG. 3 shows a bridge-type magnetoresistive sensor formed bymagnetoresistors of the type shown in FIG. 2;

FIG. 4 is a top plan view of the layout of two magnetoresistorsconfigured to detect magnetic fields directed parallel to the chip planeand perpendicular to each other;

FIG. 5 is a cross-section of a known magnetoresistive sensor having aconcentrator;

FIG. 6 is a cross-section of an embodiment of the presentmagnetoresistive sensor integrated in a semiconductor material chip;

FIG. 7 is a simplified perspective top view of the magnetoresistivesensor of FIG. 6;

FIGS. 8-10 are top plan views of different embodiments of the presentmagnetoresistive sensor;

FIGS. 11 and 12 are, respectively, a cross-section and a top plan viewof another embodiment of the present magnetoresistive sensor;

FIG. 13 is a perspective top view of a different embodiment of thepresent magnetoresistive sensor;

FIG. 14 is a cross-section of the magnetoresistive sensor of FIG. 13;

FIGS. 15A-15F are cross-sections of successive manufacturing steps ofthe magnetoresistive sensor of FIGS. 13 and 14; and

FIG. 16 is a cross-section of an embodiment of a magnetometer includingthe present integrated magnetoresistive sensor and magnetoresistivesensors for detecting magnetic fields parallel to the chip plane.

DETAILED DESCRIPTION

FIGS. 6 and 7 show a magnetoresistive sensor 30 integrated in a chip ordie 31 of semiconductor material comprising a substrate 32 and aninsulating region 33 overlying the substrate 32.

The substrate 32 has a main face 34, defining a plane XY of themagnetoresistive sensor 30. Electronic components, designated as a wholeat 35, may be provided inside and/or above the substrate 32 for readingand processing the electrical signals generated by the magnetoresistivesensor 30, in a per se known manner.

The insulating region 33 is generally formed by a plurality of layersarranged on top of each other, as described hereinafter in detail, andhouses a set/reset coil 36, at least one magnetoresistor 37 (two whereofare shown in FIGS. 6 and 7), and a concentrator 38, arranged on top ofeach other. In particular, these structures are stacked so that theset/reset coil 36 is the closest to the main face 34 and theconcentrator 38 is the furthest away from the main face 34 (the verylast component formed in the chip 31) and is arranged on top of themagnetoresistor 37. The magnetoresistor 37 is arranged between the levelof the set/reset coil 36 and the level of the concentrator 38.

In the embodiment shown, the two magnetoresistors 37 extend parallel toeach other. For example, the magnetoresistors may have a width of 2-10μm, for example 6 μm, and be arranged at the distance of 2-18 μm, forexample 6-7 μm. The two magnetoresistors 37 may be connected together inseries (in a not shown way) for forming an elementary cell, as explainedhereinafter. Alternatively, the two magnetoresistors 37 may be part of aWheatstone bridge 4 as shown in FIG. 3 and form a branch 4 a or 4 b.

The set/reset coil 36, which has the aim of carrying out refreshoperations, comprising repeated fast magnetization steps in the desireddirection, is formed in a known way by a plurality of turns 39 ofconductive material, such as aluminum or copper, whereof FIG. 7 showsthe stretches that extend (in a transverse direction) underneath themagnetoresistors 37. The turns 39 are separated from each other byinsulating portions 33 a of the insulating region 33. In the area shownin FIG. 7, then, the stretches of the turns 39 and the portions 33 a areparallel to axis X. For example, the turns 39 may have a width of 5-80μm.

Each magnetoresistor 37 comprises a magnetoresistive strip 2 having anelongated shape in the direction of the easy axis (here axis Y) andbarber poles 3. In particular, the magnetoresistive strip 2 is formed bythe superposition of two layers, and precisely a magnetoresistive layer40, such as permalloy (a ferromagnetic alloy containing iron andnickel), having a thickness of 10-70 μm, and a protective layer 41, forexample of TaN and having a thickness of 20-150 μm. In turn, the barberpoles 3 are formed by a first conductive layer 42, for example of TiWand having a thickness of 100 nm, and a second conductive layer 43, forexample of Al and having a thickness of 0.2-1 μm.

The concentrator 38 is of ferromagnetic material, for example softferromagnetic material, in particular isotropic material, such aspermalloy or other material with cobalt-iron base—such ascobalt-iron-silicon-boron (CoFeSiB) or cobalt-iron-silicon-molybdenum orcobalt-iron-silicon-niobium—such as to present a coercivity Hc close tozero (in order not to generate hysteresis/drift of the offset afterexposure to intense magnetic fields) and a permeability as high aspossible (in order to maximize the sensitivity in the direction of axisZ). Thereby, a greater concentrating effect is obtained, and it ispossible to cause the sensitivity to be independent of the properties ofthe material and thus fixed just by the geometry of the concentrator.

The concentrator 38 is here formed by a plurality of portions or bars45, which are distinct or separate from each other, have aparallelepipedal shape elongated in the direction Z, and are aligned toeach other along a midplane between the magnetoresistors 37, designatedat A in FIG. 6, so that the strips 2 of the magnetoresistors 37 aresymmetrical with respect to the concentrator 38. In particular, eachportion 45 has a width W in direction X (perpendicular to themagnetoresistors 37) smaller than the height H of the concentrator 38(in a parallel direction to axis Z). For example, the ratio W/H may beless than 1:1, for example, 6:10 or 8:15 or even less, as allowed by themanufacturing technology. The length L of the bars 45 in direction Y andthe space D between the bars 45 in the same direction (parallel to themagnetoresistors 37) is, instead, linked to the optimization of the setand reset procedure and thus depends on the design of the correspondingcoil 36, in turn optimized so as to offer an optimal load towards thecircuit for driving the reading circuit, typically an ASIC (ApplicationSpecific Integrated Circuit). Further the length L, generally greaterthan H and W, is chosen sufficiently large as to concentrate, on themagnetoresistive strips 2, a high field over a sufficiently extensivearea. In this way, it is possible to ensure a significant variation ofthe resistance due to the magnetic field directed along axis Z. Also theneeds for minimizing the area occupation may in part affect sizing of L.

In an exemplary embodiment, where the height H is determined by thethickness of the layer used for forming the concentrator 38 (asexplained in detail hereinafter), H may be comprised between 5 μm and 30μm, for example 10 μm, W may be comprised between 2 μm and 15 μm, forexample 6 μm, and L may be greater than 10 μm, for example 20-100 μm.Further, the distance D between the bars 45 may be comprised between 5μm and 16 μm.

In FIGS. 6 and 7, the magnetoresistors have barber poles 3 perpendicularto each other, at ±45° with respect to axis Y, and thus also these aresymmetrical with respect to the midplane A.

With this arrangement and with the magnetoresistors 37 connected inseries, the sensor 30 is able to detect magnetic field componentsparallel to axis Z and to cancel out the effect of possible magneticfield components coplanar to the face 34 (and thus parallel to axis X).

In fact, a magnetic-field component parallel to the positive axis Z(directed downwards) is guided in the magnetoresistors 37 in oppositedirections, causing opposite rotations of the correspondingmagnetizations and corresponding resistance variations according to thelaw:R=R _(min) +R _(d) cos²αwhere R_(min) is the magnetoresistor resistance in case of magnetizationM parallel to axis Y (easy axis), R_(d) is the resistance differenceR_(max)−R_(min), where R_(max) is the resistance in case ofmagnetization parallel to the direction X (hard axis), and a is theangle between axis Y and the current flowing in each magnetoresistor 37.

Due to the orthogonality of the directions of the barber poles 3, andthe opposite magnetization variation undergone by the twomagnetoresistors 37, the latter undergo an equal resistance variation.

Instead, a possible magnetic-field component parallel to axis X causesrotation of the magnetizations of the two magnetoresistors in the samedirection and, because of the orthogonality of the barber poles 3, anopposite variation of the resistance R. An appropriate reading circuitis thus able to discriminate the two situations and generate a usefulsignal only in the case of equal resistance variation. For example,using the Wheatstone bridge 4 of FIG. 3, with barber poles 3 arranged asillustrated, a signal is outputted only in case of magnetic fielddirected in direction Z, whereas field components directed in directionX cause a zero output voltage V₀, if the two magnetoresistors 37 form asame resistance 1 a or 1 b or form resistances 1 a or 1 b of the sametype.

Alternatively, as shown in FIG. 8, the magnetoresistors 37 of the sensor30 may have barber poles 3 parallel to each other. In this case, amagnetic field directed according to axis Z causes opposite resistancevariations in the magnetoresistors 37. Instead, a magnetic fielddirected according to axis X causes equal variations.

This solution may be used with a reading circuit requiring oppositeresistance variations for generating a useful output signal, for examplein the Wheatstone bridge 4 of FIG. 3, with the magnetoresistors 37forming the two components 1 a or the two components 1 b.

In the sensor 30 of FIGS. 6 to 8, simulations conducted by the presentapplicant have shown that the concentration effect of Z-field componentsand rejection of planar field components (in direction X) is the better,the better the alignment of the concentrator 38 with respect to themidplane (plane of symmetry) A. In fact, the magnetoresistors 37 have anexactly opposite behavior in presence of field components directed inthe direction X in case of symmetrical position of the concentrator 38,and thus in this case it is possible to directly cancel out theseeffects.

Arrangement of the concentrator 38 on top of the magnetoresistors 37 aslast component of the stack underneath the final passivation enables theconcentrator to be arranged at a small distance from themagnetoresistors 37. For example, the distance between the concentrator38 and the surface of the protective layer 41 of the magnetoresistivestrips 2 may be approximately 1 μm, or even less. Further, themanufacturing steps prior to manufacturing the concentrator 38, inparticular the thermal annealing treatments, may be studied in anoptimal way, without affecting or jeopardizing the magneticcharacteristics of the concentrator 38.

Further, the arrangement of the concentrator 38 on top of themagnetoresistors 37 enables a directed alignment between them, enablinga good reading of Z-field components and an optimal rejection ofparallel field components.

Since the concentrator 38 is arranged in a remote position from theset/reset coil 36 and is provided in a non-continuous way, a reductionof the effects of the concentrator 38 on the field generated during theset/reset step by the coil 36 is obtained.

In order to reduce further the effects of the concentrator 38 on theset/reset coil 36, it is further possible to arrange the bars 45 in thespaces between the turns 39 filled by the insulating portions 33 a ofthe insulating region 33 or in any case arrange the bars 45 centeredwith respect to the insulating portions 33 a, as shown in FIG. 9. Inpractice, the bars 45 are arranged in direction Y with the same pitch asthe turns 39 (for example, in the case of turns having a width of 30 μmand arranged at a distance of 4 μm, the have a pitch of 34 μm). In thisway, the noise caused by the concentrator 38 on the set/reset fieldgenerated by the coil 36 is substantially reduced, and simulations madeby the present applicant on the field generated on the magnetoresistors37 after a set (or reset) current pulse have shown that, with thearrangement described, it is possible to obtain an average field muchhigher as compared to the situation of a concentrator 38 formed by asingle continuous region.

In a different embodiment, in order to increase the sensitivity andreduce the cross-axis interference, the barber poles 3 may have agreater width at the spaces between the bars 45, as shown in FIG. 10.Here, alongside the bars 45, the transverse strips (designated by 3 a)have a standard width. Instead, alongside each space between the bars45, just one wider strip (designated at 3 b) is present for eachmagnetoresistor 37.

According to another embodiment, the concentrator 38 comprises two rows50 of bars 45. The two rows 50 are arranged alongside each other,symmetrical to each other and to the midplane A, and between themagnetoresistors 37, as shown in FIGS. 11 and 12. The two rows 50 arearranged very close to each other. For example, the distance between therows 50 may be of 5 μm.

The presence of two rows 50 enables increase of sensitivity of themagnetoresistive sensor 30 for a slight increase in area, since themagnetic field fluxes concentrated thereby add up, without increasingthe demagnetization factor of the bars 45, as it would be obtained byforming the bars 45 with a large width W.

In a different embodiment, shown in FIGS. 13 and 14, two shieldingregions 53, of ferromagnetic material, for example the same material asthe concentrator 38, are formed at the sides of the concentrator 38,outside the magnetoresistors 37. In detail, the shielding regions 53 areof a substantially elongated parallelepipedal shape, extending parallelto the magnetoresistors 37, and thus to axis Y, above the insulatingregion 33, at the same level of the concentrator 38. The shieldingregions 53 have a height H1 smaller than the height H of theconcentrator 38.

The shielding regions 53 enable a wider sensitivity full scale to beobtained, for a small increase of the set/reset current. A large fullscale is useful in the case of use of the magnetic sensor 30 as acompass, since the low value, Earth's magnetic field is added tomagnetic fields of a higher value, for example magnetic fields generatedby the mounting board of the compass (for example, cellphone, laptop,tablet board) due to the presence of speakers, supply lines and thelike, or interfering environmental magnetic fields, which are in generalvariable. Such interfering fields, in the direction of the easy axis,here axis Y, may give rise to undesirable reset phenomena, which,shifting the magnetization value of the bars 45 in absence of field,could considerably reduce the sensitivity.

In order to prevent the above reset phenomena from reducing thesensitivity scale of the sensor, without on the other hand interferingexcessively with the set/reset function, the non-linear behavior offerromagnetic materials is exploited, which saturate at a value ofsaturation field Hk depending upon the material and the geometricalcharacteristics, in particular upon the layer thickness (here the heightH1 of the shielding regions 53). In particular, the height H1 may bechosen in such a way that, during operation of the magnetoresistivesensor 30, the shielding regions 53 work in the linear area of thecharacteristic and thus considerably attenuate high interfering magneticfields, directed in direction Y, preventing reset effects, and insteadare in the saturation area for the higher values of magnetic field, usedin the set/reset step. For example, by choosing H=10 μm and H1=4 μm, itis possible to set a saturation limit on the shielding regions 53 at avalue of 16, 24, or 30 gauss, greater than the value of the expectedinterfering fields, but smaller than the field generated duringset/reset step, generally, of at least 50 gauss.

The magnetoresistive sensor 30 may be formed in the way described inFIGS. 15A-15F, which regards manufacturing of the magnetoresistivesensor 30 of FIGS. 13 and 14, but may be readily adapted to form theembodiments shown in FIGS. 6-12.

In detail, initially (FIG. 15A), at the end of the manufacturing stepswithin the substrate 32 and after deposition of a first insulating layer60, for example of silicon oxide, a thick metal layer 61, for example ofaluminum, is deposited and defined via photolithographic techniques, forforming the set/reset coil 36. Then a second insulating layer 62, alsofor example of silicon oxide, is deposited and is planarized via CMP(chemical mechanical polishing). The second insulating layer 62 forms,i.a., the insulating portions 33 a of the insulating region 33.

Then (FIG. 15B), the magnetoresistive layer 40, for example of permalloyor some other ferromagnetic NiFe alloy, is deposited and, thereon, theprotective layer 41, for example of TaN, is deposited for protecting themagnetoresistive layer 40 during the subsequent manufacturing steps.Then, the layers 40, 41 are defined, for forming the magnetoresistivestrips 2.

Next (FIG. 15C), the second insulating layer 62 is photolithographicallydefined for opening vias 63 as far as the metal layer 61. Then the firstconductive layer 42, for example of TiW, and the second conductive layer43, for example of Al, are deposited and photolithographically definedfor forming the barber poles 3 and contact pads 65 in the vias 63.

Next (FIG. 15D), a third insulating layer 66, for example of siliconoxide, is deposited and planarized via CMP, thus forming, together withthe first and second insulating layers 60, 62, the insulating region 33.The insulating region 33 thus has a planar surface parallel to the face34. A seed layer 67, for example with a thickness of 100-200 nm, isdeposited on the insulating region 33. For the embodiment of FIGS. 13and 14, the shielding regions 53 are then formed on the seed layer 67 bydefining the corresponding area and by electrolytic deposition growth,in a per se known manner.

Then (FIG. 15E), the concentrator 38 is formed by defining thecorresponding area and selective, electrolytic deposition growth, in away in per se known manner. In particular, in this step, there is growthof the plurality of bars 45 shown, for example, in FIG. 7.

Finally, FIG. 15F, the seed layer 67 is etched and selectively removedfrom the surface of the insulating region 33, a passivation layer 70,for example of silicon oxide or nitride, is formed, and the passivationand insulating layers are removed at the contact pads 65.

In this way, the temperatures and techniques for forming the metal layer61 and of the insulating region 33 of silicon oxide do not adverselyaffect the magnetic properties of the ferromagnetic material of theconcentrator 38. The magnetoresistive sensor 30 sensitive to magneticfields directed perpendicular to the chip may be formed in a single chipwith sensors sensitive to magnetic fields directed along axes X and Y,i.e., planar with respect to the chip. In particular, FIG. 16 shows achip 80 integrating the magnetoresistive sensor 30 of FIG. 6, sensitiveto magnetic fields parallel to axis Z, a first planar sensor 81,sensitive to magnetic fields parallel to axis X, and a second planarsensor 82, sensitive to magnetic fields parallel to axis Y. The sensors81 and 82 are formed with the same technology used for themagnetoresistive sensor 30 and thus have respective set/reset coils 84,85, formed in the metal layer 61, magnetoresistive strips 2 formed bythe layers 40 and 41, and barber poles 3 formed by the conductive layers42 and 43. Alternatively, the set/reset coils may be in common, in aknown manner for biaxial sensors.

All three sensors 30, 81, 82 may comprise a plurality ofmagnetoresistors 37, connected for forming three Wheatstone bridges, asshown in FIG. 3 and as described above.

In this way, it is possible to provide a triaxial sensor or magnetometerintegrated in a single chip 80. The described sensor has a highsensitivity and high resolution in all three directions and may bemanufactured so as to overcome the yield and cost difficulties existingin some situations in the manufacture of the Z sensor.

The manufacturing process is particularly simple and far from costly, ascompared with the currently used processes.

The architecture is very reliable in so far as the concentrator does notundergo thermal treatments that could jeopardize functionality thereof,and its manufacture is highly repeatable. Any possible problems ofmisalignment are not critical for proper operation.

Using the solution having shielding regions 53, it is possible to extendthe sensitivity full scale, with a reduced impact on the set/resetcurrents, and thus on the consumption of the sensor.

Finally, it is clear that modifications and variations may be made tothe magnetoresistive sensor described and illustrated herein and to thecorresponding manufacturing method, without thereby departing from thescope of the present disclosure.

For example, even though the Z-magnetoresistive sensor is shown in thedrawings parallel to axis X, it may be parallel to axis Y, or have anyangle with respect to axes X, Y of the plane. Further, in the case ofmore pairs of magnetoresistors 37, these may even not be parallel toeach other, but be arranged in the most useful way, for example so as totake into account layout requirements in the chip.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. An AMR-type integrated magnetoresistivesensor sensitive to perpendicular magnetic fields, comprising: a body ofsemiconductor material, having a face extending in a plane and defininga first and a second direction; an insulating region on the face of thebody; a set/reset coil arranged within the insulating region; a firstmagnetoresistor arranged within the insulating region and on theset/reset coil and including an elongated first magnetoresistive stripextending longitudinally parallel to the first direction; and aconcentrator of ferromagnetic material, arranged on the insulatingregion and formed by a plurality of distinct ferromagnetic bars alignedwith each other parallel to the first direction and spaced apart fromeach other, wherein the ferromagnetic bars have each a substantiallyparallelepiped shape with a height in a third direction perpendicular tothe face and a width in the second direction, wherein the height isgreater than the width.
 2. The magnetoresistive sensor according toclaim 1, wherein a ratio of the width to height is less than 1:1.
 3. Themagnetoresistive sensor according to claim 2, wherein the ratio isbetween 6:10 and 8:15.
 4. The magnetoresistive sensor according to claim1, wherein the set/reset coil comprises a plurality of turns havingstretches directed transversely to the first direction and spaced apartfrom each other via portions of the insulating region, wherein theferromagnetic bars are arranged approximately centered on the portionsof the insulating region.
 5. The magnetoresistive sensor according toclaim 1, wherein the first magnetoresistor has barber poles overlaid tothe magnetoresistive strip and directed transversely to the first andsecond directions, the barber poles having respective widths that areequal to each other.
 6. The magnetoresistive sensor according to claim1, wherein the first magnetoresistor has barber poles overlaid to thefirst magnetoresistive strip and directed transversely to the first andsecond directions, the barber poles having respective widths in thefirst direction, with barber poles of smaller width alongside theferromagnetic bars of the concentrator and barber poles of greater widthalongside spaces between the ferromagnetic bars.
 7. The magnetoresistivesensor according to claim 1, comprising a second magnetoresistorarranged within the insulating region and on the set/reset coil, thesecond magnetoresistor including an elongated second magnetoresistivestrip extending longitudinally parallel to the first direction andlaterally spaced apart from the first magnetoresistive strip; theconcentrator extending substantially along a midplane between the firstand second magnetoresistors.
 8. The magnetoresistive sensor according toclaim 7, wherein the first and second magnetoresistors have barber polesoverlaying the respective magnetoresistive strips and directedtransversely to the first and second directions, parallel orperpendicular to each other.
 9. The magnetoresistive sensor according toclaim 8, wherein the concentrator comprises two distinct rows offerromagnetic bars, the two rows being arranged alongside each other andeach being arranged on an opposite side of the midplane, symmetricallywith respect to each other, between the first and secondmagnetoresistors.
 10. The magnetoresistive sensor according to claim 7,comprising shielding regions of ferromagnetic material arranged on theinsulating region and extending parallel to the first direction outsidethe magnetoresistive regions, the shielding regions having a smallerheight than the concentrator.
 11. The magnetoresistive sensor accordingto claim 1, comprising a plurality of magnetoresistors connected to forma Wheatstone bridge, each magnetoresistor including a magnetoresistivestrip, the plurality of magnetoresistors including the firstmagnetoresistor.
 12. An AMR-type triaxial magnetometer, comprising: abody of semiconductor material, having a face extending in a plane anddefining a first and a second direction; an insulating region on theface of the body; an integrated first magnetoresistive sensor sensitiveto perpendicular magnetic fields, the first magnetoresistive sensorincluding: a set/reset coil arranged within the insulating region; afirst magnetoresistor arranged within the insulating region and on theset/reset coil and including an elongated first magnetoresistive stripextending longitudinally parallel to the first direction; and aconcentrator of ferromagnetic material, arranged on the insulatingregion and formed by a plurality of distinct ferromagnetic bars alignedwith each other parallel to the first direction and spaced apart fromeach other; a planar second magnetoresistive sensor having sensitivityaccording to a first axis parallel to the plane; and a planar thirdmagnetoresistive sensor having sensitivity according to a second axisperpendicular to the first axis, wherein the ferromagnetic bars haveeach a substantially parallelepiped shape with a height in a thirddirection perpendicular to the face and a width in the second direction,wherein the height is greater than the width.
 13. The triaxialmagnetometer according to claim 12, wherein the set/reset coil comprisesa plurality of turns having stretches directed transversely to the firstdirection and spaced apart from each other via portions of theinsulating region, wherein the ferromagnetic bars are arrangedapproximately centered on the portions of the insulating region.
 14. Thetriaxial magnetometer according to claim 12, wherein the firstmagnetoresistor has barber poles overlaid to the first magnetoresistivestrip and directed transversely to the first and second directions, thebarber poles having respective widths in the first direction, withbarber poles of smaller width alongside the ferromagnetic bars of theconcentrator and barber poles of greater width alongside spaces betweenthe ferromagnetic bars.
 15. The triaxial magnetometer according to claim12, wherein the first magnetoresistive sensor includes a secondmagnetoresistor arranged within the insulating region and on theset/reset coil, the second magnetoresistor including an elongated secondmagnetoresistive strip extending longitudinally parallel to the firstdirection and laterally spaced apart from the first magnetoresistivestrip; the concentrator extending substantially along a midplane betweenthe first and second magnetoresistors.
 16. An AMR-type integratedmagnetoresistive sensor sensitive to perpendicular magnetic fields,comprising: an insulating body; a set/reset coil arranged within theinsulating body; elongated first and second magnetoresistor stripsarranged within the insulating body and above the set/reset coil, thefirst and second magnetoresistive strips extending longitudinallyparallel to each other; and a first plurality of distinct ferromagneticconcentrator bars spaced apart from each other and aligned with eachother in a first direction parallel to the first and secondmagnetoresistor strips and arranged on the insulating region, theconcentrator bars extending upwardly directly above a region of theinsulating body between the first and second magnetoresistor strips,wherein the ferromagnetic concentrator bars have each a substantiallyparallelepiped shape with a height in a second direction, perpendicularto a face of the insulating body from which the ferromagneticconcentrator regions extend, and a width in a third directionperpendicular to the first direction, wherein the height is greater thanthe width.
 17. The magnetoresistive sensor according to claim 16,wherein the set/reset coil comprises a plurality of turns havingstretches directed transversely to the first direction and spaced apartfrom each other via portions of the insulating body, wherein theferromagnetic concentrator bars are arranged approximately centered onthe portions of the insulating body.
 18. The magnetoresistive sensoraccording to claim 16, further comprising barber poles overlaid to thefirst magnetoresistive strip and extending transversely to the firstdirection, the barber poles having respective widths in the firstdirection, with barber poles of smaller width alongside theferromagnetic concentrator bars and barber poles of greater widthalongside spaces between the ferromagnetic concentrator bars.
 19. Themagnetoresistive sensor according to claim 18, further comprising asecond plurality of distinct ferromagnetic concentrator bars alignedwith each other in a second direction parallel to the first direction,the first and second pluralities of distinct ferromagnetic concentratorbars being arranged alongside each other and each being arranged on anopposite side of a midplane, symmetrically with respect to each other,between the first and second magnetoresistor strips.
 20. An AMR-typeintegrated magnetoresistive sensor sensitive to perpendicular magneticfields, comprising: a body of semiconductor material, having a faceextending in a plane and defining a first and a second direction; aninsulating region on the face of the body; a set/reset coil arrangedwithin the insulating region; a first magnetoresistor arranged withinthe insulating region and on the set/reset coil and including anelongated first magnetoresistive strip extending longitudinally parallelto the first direction; and a concentrator of ferromagnetic material,arranged on the insulating region and formed by a plurality of distinctferromagnetic bars aligned with each other parallel to the firstdirection and spaced apart from each other, wherein the set/reset coilcomprises a plurality of turns having stretches directed transversely tothe first direction and spaced apart from each other via portions of theinsulating region, wherein the ferromagnetic bars are arrangedapproximately centered on the portions of the insulating region.
 21. Themagnetoresistive sensor according to claim 20, wherein the firstmagnetoresistor has barber poles overlaid to the magnetoresistive stripand directed transversely to the first and second directions, the barberpoles having respective widths that are equal to each other.
 22. Themagnetoresistive sensor according to claim 20, comprising a secondmagnetoresistor arranged within the insulating region and on theset/reset coil, the second magnetoresistor including an elongated secondmagnetoresistive strip extending longitudinally parallel to the firstdirection and laterally spaced apart from the first magnetoresistivestrip; the concentrator extending substantially along a midplane betweenthe first and second magnetoresistors.
 23. An AMR-type integratedmagnetoresistive sensor sensitive to perpendicular magnetic fields,comprising: an insulating body; a set/reset coil arranged within theinsulating body; elongated first and second magnetoresistor stripsarranged within the insulating body and above the set/reset coil, thefirst and second magnetoresistive strips extending longitudinallyparallel to each other; and a first plurality of distinct ferromagneticconcentrator bars spaced apart from each other and aligned with eachother in a first direction parallel to the first and secondmagnetoresistor strips and arranged on the insulating region, theconcentrator bars extending upwardly directly above a region of theinsulating body between the first and second magnetoresistor strips,wherein the set/reset coil comprises a plurality of turns havingstretches directed transversely to the first direction and spaced apartfrom each other via portions of the insulating body, wherein theferromagnetic concentrator bars are arranged approximately centered onthe portions of the insulating body.
 24. The magnetoresistive sensoraccording to claim 23, further comprising barber poles overlaid to thefirst magnetoresistive strip and extending transversely to the firstdirection, the barber poles having respective widths in the firstdirection, with barber poles of smaller width alongside theferromagnetic concentrator bars and barber poles of greater widthalongside spaces between the ferromagnetic concentrator bars.
 25. Themagnetoresistive sensor according to claim 23, further comprising asecond plurality of distinct ferromagnetic concentrator bars alignedwith each other in a second direction parallel to the first direction,the first and second pluralities of distinct ferromagnetic concentratorbars being arranged alongside each other and each being arranged on anopposite side of a midplane, symmetrically with respect to each other,between the first and second magnetoresistor strips.